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A silver-oxide battery (IEC code: S) is a primary cell with a very high energy-to-weight ratio. They are available in small sizes as button cells, where the amount of silver used is minimal and not a significant contributor to the product cost.
Silver oxide cells
|Specific energy||130 Wh/kg|
|Energy density||500 Wh/L|
Silver-oxide primary batteries account for over 20% of all primary battery sales in Japan (67,000 out of 232,000 in September 2012).
A silver-oxide battery uses silver(I) oxide as the positive electrode (cathode), zinc as the negative electrode (anode), plus an alkaline electrolyte, usually sodium hydroxide (NaOH) or potassium hydroxide (KOH). The silver is reduced at the cathode from Ag(I) to Ag, and the zinc is oxidized from Zn to Zn(II).
The half-cell reaction at the negative plate:
The reaction in the electrolyte:
The half-cell reaction at the positive plate:
Overall reaction (anhydrous form):
Silver-oxide batteries become hazardous on the onset of leakage; this generally takes 5 years from the time they are put into use (which coincides with their normal shelf life). Until recently, all silver-oxide batteries contained up to 0.2% mercury. The mercury was incorporated into the zinc anode to inhibit corrosion in the alkaline environment. Sony started producing the first silver-oxide batteries without added mercury in 2004.
- "ProCell Silver Oxide battery chemistry". Duracell. Archived from the original on 2009-12-20. Retrieved 2009-04-21.
-  Monthly battery sales statistics - MoETI - March 2011.
- World’s First Environmentally Friendly Mercury Free Silver Oxide Batter. September 29, 2004.
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